The present invention relates to a method to control a hybrid powertrain in a vehicle, to a hybrid powertrain, which comprises elements to control the method, and also a vehicle, which comprises such a hybrid powertrain.
Some trucks are equipped with a transmission of both an automatic and a manual type. With this type of transmission, shifting is carried out from a first gear to a second gear by bringing the gearbox from one torque state in the powertrain to a substantially zero torque state, subsequently disengaging the current gear, and subsequently synchronizing the input shaft's speed and the lay shaft's speed to a speed corresponding to the second gear. Subsequently, the second gear is engaged, followed by bringing the gearbox to a powertrain torque state requested by the driver.
The vehicle may be powered by a combustion engine and an electric machine, which interact to produce the desired output and to, among other things, achieve good fuel economy in the vehicle. The electric machine may, at acceleration and constant speed of the vehicle, function as an electric engine. At deceleration of the vehicle, the electric machine may function as a generator and exert a braking torque on the vehicle's powertrain.
In the powertrain, there are gaps between the components interacting in the transmission, arising e.g. as a result of backlash among cogwheels in engagement. There is also a torsion spring effect in the rotatable shafts in the powertrain. The gaps and the torsion spring effect become most evident when the gearbox is brought to a powertrain torque state from a substantially zero torque state. In the event the electric machine is accelerated or decelerated after a second gear has been engaged, the gaps and resilient shafts will cause a pulse and a shock wave in the hybrid powertrain, which will be experienced as a disturbance by the driver and passengers in the vehicle. The pulse and the shock wave may also elicit a swinging in the hybrid powertrain because of the torsion spring effect of the shafts. This swinging will also be perceived as uncomfortable by the vehicle's driver and passengers.
After the second gear has been engaged and torque is supplied to the transmission, there is no guarantee that the combustion engine will be operated at the speed required for it to be connected and supply torque to the transmission. Therefore, time is needed to control the combustion engine to the desired speed and torque.
WO 2011141233, A1 shows a vehicle equipped with a hybrid powertrain, which comprises a combustion engine and an electric machine. At shifting, the electric machine's moment of inertia is used for synchronization. Thus, synchronization rings in the gearbox may be eliminated.